Seismic surveying techniques use reflected seismic waves to determine underground geologic structure. One manner of seismic surveying uses an active source to generate one or more controlled seismic waves. The active source may, for example, be an explosive, an air gun or a vibrator truck. The seismic waves generated by the active source are reflected off of underground geologic structure, and the reflected seismic waves are typically recorded by a plurality of receivers such as seismic motion sensors, geophones, accelerometers, or hydrophones. The recordings may be vertical ground motion (velocity or acceleration), pressure, components (e.g. three directions) of ground motion or a combination thereof. Seismic data processing methods are then used to process the recorded response and produce an image of underground geologic structure therefrom.
Seismic interferometry is a method of seismic data collection and manipulation or processing that is able to use a receiver as a virtual source to simulate and replace an active source. Typically, seismic waves are recorded at a primary location (the virtual source location). The seismic waves recorded at the primary location may be deliberate or non-deliberate seismic waves present in the earth such as, for example, natural background seismic waves due to ocean wave action, seismic waves due to vehicle traffic, or even seismic waves caused by a remotely positioned active source. At the same time, seismic waves are also recorded at least one additional location, a secondary location of the seismic interferometry process. The time series recorded at the secondary location is deconvolved using the time series recorded at the virtual source location. In instances where the receivers measure multiple components of ground motion, the deconvolution is performed between each of the components. Since the seismic waves recorded at the virtual source location are reflected from the surface of the earth, a portion of these reflected seismic waves will reflect off of underground geologic structure and reach the additional location. In this regard, the deconvolution of the components of the time series recorded at the secondary location contains the same response as there would be if there was a source for each of the ground motion components at the primary location generating seismic waves being recorded by a receiver at the additional location. Thus, this seismic interferometry data may substitute for conventional active seismic source data. Active source seismic data processing methods may then be used to produce an image of underground geologic structure in a manner similar to active source seismic surveying.